[libc][math] fmod: clear exceptions before the test instead of after

The test has no control over the CPU state before the test runs.

This test checks whether no exception flags are set, which may not be
true at the start of the test. This used to be not a problem because the
check was broken but that was fixed in ecfb5d9

libc/test/src/math/FModTest.h

@@ -18,10 +18,10 @@
 #include "hdr/math_macros.h"
 
 #define TEST_SPECIAL(x, y, expected, dom_err, expected_exception)              \
+  LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT);                         \
   EXPECT_FP_EQ(expected, f(x, y));                                             \
   EXPECT_MATH_ERRNO((dom_err) ? EDOM : 0);                                     \
-  EXPECT_FP_EXCEPTION(expected_exception);                                     \
-  LIBC_NAMESPACE::fputil::clear_except(FE_ALL_EXCEPT)
+  EXPECT_FP_EXCEPTION(expected_exception)
 
 #define TEST_REGULAR(x, y, expected) TEST_SPECIAL(x, y, expected, false, 0)